1. Field of the Invention
The present invention relates to an image transfer sheet containing a support, a barrier layer, a polyester layer, and an optional sublimation based colorant (i.e. dyes, ink, toners, etc.; hereinafter “sublimation dye”) receiving layer and, and methods for transferring an image to a receptor element using the image transfer sheet. More specifically, the present invention relates to an image transfer sheet which can be applied to a receptor element, such as cotton or cotton/polyester blend fabrics or the like (e.g. wood, nylon, ceramics, etc.).
2. Description of the Prior Art
Textiles such as shirts (e.g., tee shirts) having a variety of designs thereon have become very popular in recent years. One technique used for decorating various textiles has been the sublimation dye printing technique. In sublimation printing, a design is printed on a paper backing sheet by conventional printing techniques using sublimation dyes, and then the design is transferred to a substrate under heat and pressure. Sublimation dye printing generally results in colors which stay bright during the heat transfer process.
Prior attempts to use sublimation dye in transfer designs to be applied to 100% cotton or high content cotton (i.e. 50% or more cotton) in cotton/polyester blend fabrics have resulted in distorted and faded colors. Attempts to overcome this problem have included two-step processes wherein the fabric to be printed is pretreated with an emulsion which would be more receptive to sublimation dyes. The printed image is then transferred to the treated fabric. The two-step process prevents the average consumer from using sublimation colorant printing techniques, since commercial facilities are required for the pre-treating and transferring steps.
PCT/US00/29796 relates to an image transfer sheet containing a support, a barrier layer, a sublimation dye layer and a polyester layer, and a method for transferring an image to a receptor element using the image transfer sheet. More specifically, it relates to an image transfer sheet which can be applied to a receptor element, such as cotton or cotton/polyester blend fabrics or the like.
U.S. Pat. No. 4,021,591 is directed to a dry release sublimation transfer element and to a method for decorating a substrate using the transfer element. The sublimation design layer has a thickness in the range of 0.1 to 3 mils.
U.S. Pat. No. 4,555,436 is directed to a heat transferable laminate comprising a support layer, a transfer layer, an ink design layer and an adhesive. The ink design layer is composed of conventional inks.
U.S. Pat. No. 4,657,557 relates to sublimation transfer sheets consisting of a base coated with a sublimation ink, further coated with a heat-resistant resin. A barrier layer is not employed in the sheets.
U.S. Pat. No. 4,914,079 is directed to a thermal transfer ink medium containing a support, an ink layer and an ink transfer layer. A barrier layer is not incorporated into the medium.
U.S. Pat. No. 4,927,709 is directed to a heat transferable laminate comprising a support layer, a transfer layer, an ink design layer and an adhesive. The ink design layer is composed of conventional inks.
U.S. Pat. No. 4,935,300 is directed to a heat transferable laminate comprising a support layer, a transfer layer, an ink design layer and an adhesive. The ink design layer is composed of conventional inks.
U.S. Pat. No. 5,322,833 relates to a dye-donor element for use in thermal sublimation dye transfers.
U.S. Pat. No. 5,413,841 is directed to heat activated transfer elements comprising a lower adhesive layer and an upper thermoset layer which contains an indicia layer formed from sublimation dyes. The thermosetting layers do not comprise thermally activated polymers.
U.S. Pat. No. 5,679,461 relates to thermally sensitive transfer recording materials comprising a base sheet, an ink layer and an ink-resistant lubricating layer. A barrier layer is not present between the ink layer and the lubricating layer.
U.S. Pat. No. 5,741,387 is directed to a lithographic printing process and transfer sheet comprising a backing sheet, a heat release layer, an ink design layer, a polymer layer and a lacquer mask layer. The ink design layer is composed of conventional inks which are described as being heat-resistant.
U.S. Pat. No. 6,143,454 relates to a color thermal transfer sublimation dye toner comprising at least a binder resin and a sublimation dye component, the binder resin comprising a high molecular weight polymer having a molecular weight of above about 100,000, and the sublimation colorant comprising a dye which sublimes at elevated temperatures above about 100° C.
When matter directly changes state from a highly organized solid state to an unorganized gas state, without going through the semi-ordered liquid state, such a change of state is referred to as sublimation. Whether matter sublimates depends on the chemical properties of the matter, and more importantly, on both the pressure and temperature of the system. Some materials have the property of being able to undergo sublimation under atmospheric pressure and elevated temperatures. Dry ice, or solid carbon dioxide, is one such material that undergoes sublimation at atmospheric pressure and room temperature. For dry ice, room temperature is said to be above the sublimation temperature of solid carbon dioxide at atmospheric pressure. As the temperature is raised above the sublimation temperature, the material undergoes a direct solid to gas phase transition since the material is given sufficient thermal energy to break inter-molecular attractions operative in a liquid state. Not all matter exhibits this property. In contrast, water is a form of matter that when heated under atmospheric pressure conditions, has chemical properties consistent with solid to liquid to gas phase transitions. Solid water (ice) may also sublimate, but only at pressures far below atmospheric pressure.
Another class of material that exhibit both sublimation properties and color are known as sublimation colorants or dyes. Sublimation dyes, like dry ice, have chemical properties such that, when heated under near-atmospheric conditions, they sublimate or undergo a direct solid to gas phase transition. The sublimation temperature for a number of these dyes resides anywhere from just above room temperature to as high as the chemical decomposition temperature for organic systems such as 400° C. The important property that makes these colorants useful in printing applications is that, at these temperatures, sublimation dyes sublime under near atmospheric pressure conditions.
These sublimation colorants are used in a variety of ink formulations each targeted for a specific printing method. They are typically found as the colorant in offset or lithographic ink mixtures. However, these colorants have also been mixed into formulations used for the newer electronic printing methods. The largest market for sublimation dyes is found in thermal ribbon printing for label and point-of-sale applications. With thermal printing, the sublimation colorant is dispersed into a wax or polyester binder formulation and coated onto a polyester or cloth ribbon. A mark is made on the receptor substrate by heating the back of the ribbon with a metal stylus and subliming the dye off the ribbon onto the receptor. This process is rather slow in comparison to other modes of printing. Sublimation dyes have been formulated into toner mixtures used for the higher speed laser, electrostatic and/or electrophotographic printing applications as described in U.S. Pat. No. 6,143,454. Sublimation dyes have also been added to formulations used for the newer ink jet process as described in U.S. Pat. No. 5,830,263. With the ink jet or laser printing applications, the sublimation dye is printed on a temporary receptor which will later be reheated to transfer the image-wise mark to a final receptor. In all these applications, where sublimation dyes are used as the colorants, the process by which the dye colors the final receptor is the same; yet, the printing methods are different.
The receptor for sublimation dyes is a support of many types, such as paper, films or fabrics, that is either composed of or coated with a polymer known as a polyester. The term and polymers referred to as polyesters are well known to those skilled in the art. Polyesters are used as the receptor for sublimation dyes. Many polyesters undergo a secondary phase transition that attract the dyes to enter and become trapped within the molecular framework of the polymer. This secondary phase transition occurs at about the same temperature and pressure as the printing dyes sublimate. A secondary phase transition refers to a reversible change in shape or structure in difference to a primary change of state such as ice melting. As both the colorant and receptor are heated, the polyester changes to an “open” conformation as the dye begins to sublimate and enters the structure. As heat energy is removed, the reverse process occurs and the polymer undergoes a “closed” conformational change locking and trapping the dye within the polymer structure. The overall effect of the dye-polymer interaction is one of becoming attracted, trapped and caged. Many polymers cannot exhibit such a secondary phase transition, and therefore, cannot attract and trap the dye within. One such polymer is natural cotton. Sublimation dyes will neither be attracted to or bind within a fiber of cotton. Therefore, when fabrics are used as the receptor for sublimation printing, such fabrics (like t-shirts or banners), are either 100% polyester or a cotton/high polyester blend fabric containing sufficient polyester in the fabric to allow the sublimation dyes to be attracted and bind to the fabric blend. Untreated cotton makes a poor receptor for sublimation dyes.